# std::strtof, std::strtod, std::strtold

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< cpp‎ | string‎ | byte

Defined in header `<cstdlib>` |  |
float strtof ( const char* str, char** str_end ); | (1) | (since C++11)
double strtod ( const char* str, char** str_end ); | (2) |
long double strtold( const char* str, char** str_end ); | (3) | (since C++11)

Interprets a floating point value in a byte string pointed to by str.

Function discards any whitespace characters (as determined by std::isspace) until first non-whitespace character is found. Then it takes as many characters as possible to form a valid floating-point representation and converts them to a floating-point value. The valid floating-point value can be one of the following:

- decimal floating-point expression. It consists of the following parts:

  - (optional) plus or minus sign
  - nonempty sequence of decimal digits optionally containing decimal-point character (as determined by the current C locale) (defines significand)
  - (optional) `e` or `E` followed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent to base 10)

hexadecimal floating-point expression. It consists of the following parts: (optional) plus or minus sign `0x` or `0X` nonempty sequence of hexadecimal digits optionally containing a decimal-point character (as determined by the current C locale) (defines significand) (optional) `p` or `P` followed with optional minus or plus sign and nonempty sequence of decimal digits (defines exponent to base 2) infinity expression. It consists of the following parts: (optional) plus or minus sign `INF` or `INFINITY` ignoring case not-a-number expression. It consists of the following parts: (optional) plus or minus sign `NAN` or `NAN(`char_sequence`)` ignoring case of the `NAN` part. char_sequence can only contain digits, Latin letters, and underscores. The result is a quiet NaN floating-point value. | (since C++11)

- any other expression that may be accepted by the currently installed C locale

The functions sets the pointer pointed to by str_end to point to the character past the last character interpreted. If str_end is a null pointer, it is ignored.

### Parameters

str | - | pointer to the null-terminated byte string to be interpreted
str_end | - | pointer to a pointer to character.

### Return value

Floating point value corresponding to the contents of str on success. If the converted value falls out of range of corresponding return type, range error occurs and HUGE_VAL, HUGE_VALF or HUGE_VALL is returned. If no conversion can be performed, ​0​ is returned and *str_end is set to str.

### Example

Run this code

    #include <cerrno>
    #include <clocale>
    #include <cstdlib>
    #include <iostream>
    #include <string>

    int main()
    {
        const char* p = "111.11 -2.22 0X1.BC70A3D70A3D7P+6 -Inf 1.18973e+4932zzz";
        char* end{};
        std::cout << "Parsing \"" << p << "\":\n";
        errno = 0;
        for (double f = std::strtod(p, &end); p != end; f = std::strtod(p, &end))
        {
            std::cout << "  '" << std::string(p, end - p) << "' -> ";
            p = end;
            if (errno == ERANGE)
            {
                std::cout << "range error, got ";
                errno = 0;
            }
            std::cout << f << '\n';
        }

        if (std::setlocale(LC_NUMERIC, "de_DE.utf8"))
        {
            std::cout << "With de_DE.utf8 locale:\n";
            std::cout << "  '123.45' -> " << std::strtod("123.45", 0) << '\n';
            std::cout << "  '123,45' -> " << std::strtod("123,45", 0) << '\n';
        }
    }

Possible output:

    Parsing "111.11 -2.22 0X1.BC70A3D70A3D7P+6 -Inf 1.18973e+4932zzz":
      '111.11' -> 111.11
      ' -2.22' -> -2.22
      ' 0X1.BC70A3D70A3D7P+6' -> 111.11
      ' -Inf' -> -inf
      ' 1.18973e+4932' -> range error, got inf
    With de_DE.utf8 locale:
      '123.45' -> 123
      '123,45' -> 123.45

### See also

atof | converts a byte string to a floating point value (function)
wcstofwcstodwcstold | converts a wide string to a floating-point value (function)
from_chars (C++17) | converts a character sequence to an integer or floating-point value (function)
C documentation for strtof, strtod, strtold

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